This invention relates to hydraulic control apparatus for a clutch, especially for a motor vehicle, including at least one emitter or receiver cylinder having a piston.
More particularly, the invention relates to hydraulic control apparatus of the type described in French patent application No. 99 02426, for a motor vehicle clutch, and of the type in which the cylinder body includes, arranged in consecutive axial succession from front to rear, at least one blind front part which includes the said base portion, and a central part which carries the said at least one sealing ring, the said parts being fixed together sealingly, and of the type in which the said internal bore includes two portions for guiding the piston in axial sliding movement, namely a front portion and a rear portion substantially coaxial and concentric with each other.
In that document, the cylinder body is in three parts, namely a front part, a central part and a rear part respectively, which are moulded, in particular in plastics material, and the two portions whereby the piston is guided in axial sliding movement in the internal bore of the cylinder body are formed by precision moulding in the front part and in the rear part respectively.
Apart from the manufacturing costs that result from manufacture of the front and rear parts, in which precision is important for the production of the guide portions for axial sliding movement of the piston, this design is also complicated and expensive because the assembly and fastening of the front and rear parts on the central part must be carried out to an equally high degree of accuracy in order to ensure that the front and rear portions that guide the piston in axial sliding movement are properly coaxial and concentric.
In order to overcome these drawbacks, and particularly in order to reduce even more the manufacturing and quantity production assembly costs, the invention proposes a control apparatus of the type mentioned above, characterised in that the front portion and rear portion for guiding the piston in sliding movement are comprised in the central part of the cylinder body.
According to further features of the invention:
the rear guide portion is formed directly in the central part of the cylinder body, and the front guide portion is formed in an internal central guide sleeve attached in the central part;
the central part and the guide sleeve include means for positioning and centring the sleeve with respect to the central part so as to ensure that the front guide portion and rear guide portion are coaxial and concentric with each other;
the means for positioning and centring the sleeve with respect to the central part comprise a cylindrical centring surface and a radially oriented transverse axial positioning face of the centring sleeve, cooperating with a complementary cylindrical centring surface and a radially oriented transverse axial positioning face of the central part;
the centring sleeve is attached in the central part by axial introduction from front to rear;
the cylindrical centring surface of the centring sleeve is a convex surface, and the radially oriented axial positioning transverse face of the centring sleeve is oriented axially towards the rear;
the central part has a stepped internal bore which comprises at least one rear portion of smaller diameter, constituting the said rear portion for guiding the piston in sliding movement, and at least one front portion, the internal surface of which constitutes the concave cylindrical centring surface of the central part;
the said at least one sealing ring is interposed axially between a radially oriented transverse face of the central part, and a radially oriented transverse rear end face of the centring sleeve;
the said at least one sealing ring is mounted in an intermediate portion of the stepped bore which is delimited axially, with respect to the said rear portion having the smaller diameter, by a shoulder that constitutes the said radially oriented transverse face of the central part;
the apparatus has two sealing rings, namely a front ring and a rear ring, which are interposed axially between the said radially oriented rear transverse face of the central part and the said transverse front end face of the guide sleeve, with a spacer being interposed between the two sealing rings;
the cylinder body comprises a front part, which is open axially towards the rear and is fixed to the rear of the central part;
the rear part is formed integrally and in one piece with the central part;
the rear part is fixed on the rear portion of the central part by resilient insertion;
the central part is moulded in plastics material;
the guide sleeve is moulded in plastics material;
the front part and central part are welded together sealingly by indirect heating;
the centring sleeve and the central part are welded together by indirect heating;
the central part of the cylinder body is configured as a transverse plate for fastening the control apparatus;
the rear end of the cylinder body includes at least one abutment adapted to cooperate with a rear end of the piston, for limiting axial rearward displacement of the piston;
the piston includes a peripheral piston jacket of metal, which is fixed axially to the piston and which slides axially in the internal bore of the cylinder body.